The present invention relates to a plasma processing apparatus for processing wafers or similar objects with neutral particles produced from plasma.
In the semiconductor devices art, dry etching is extensively used to process wafers or similar objects accurately. It is a common practice with a dry etching apparatus to excite etching gas by a high frequency power source so as to generate plasma. Chemically active particles produced from the plasma are incident upon the surface of a wafer in the form of a beam. Among the active particles, ions are accelerated by an electric field and caused to impinge on the surface of the wafer. This implements highly anisotropic etching and allows patterns to be processed with accuracy. However, the problem with etching using charged ions is that the surface of the wafer charged and destroys a semiconductor device due to the charge-up thereof, thereby degrading the reliability of such a device. Therefore, to effect reliable etching while insuring high anisotropy, active particles of the same orientation and electrically neutral are essential.
A conventional plasma processing apparatus of the kind etching an object with neutral active particles is disclosed in, for example, Japanese Patent Laid-Open Publication No. 4-343421. This kind of apparatus has a plasma chamber into which etching gas is admitted in order to generate plasma, an etching chamber for etching an object disposed therein with neutral particles produced from the plasma, and a micro channel plate separating such two chambers and formed with micro channels for allowing the neutral particles from moving from the plasma chamber to the etching chamber in the form of a neutral beam. With such an apparatus, however, a sufficient plasma density is not achievable in the plasma chamber. Hence, the density of ions and that of active particles available with the apparatus are too low to meet the increasing demand for higher etching speeds or processing speeds.